Electric phonograph reproducer



A. A. THOMAS ELECTROMAGNETIC TRANSLATING DEVICE ELECTRIC PHONOGRAPH REPRODUCER EiledDec. 50. 1925 May 31, 1927. E 1.630,640

INVENTDR Patented May 31, 1927.

UNITED STATES I 1, 30,640 PATENT OFFICE.

-ADOLIEH A. THOMAS, OF NEW YORK, N. Y.

Application filed December 30, 1925.

My invention relates to sound-reproducing devices. and its object is to provide a new and improved sound reproducer particularly adapted for use in phonographs and similar apparatus.

The electric reproducer of ,my invention comprises a vibratory arm mechanically actuated at one end and carrying at its other end a magnetic member arranged to coop- 10 .erate with electromagnetic mechanism to generate current impulses in accordance with the vibrations of the arm. WVhen my invention is embodied as a phonograph reproducer, the vibratory arm is actuated at one end by a record needle, and the vibrations of the needle are transmitted to the magnetic member in amplified ratio. In the broader aspect of my invention, the vibratory arm may be mechanically actuated by any other acoustic means for electrically reproducing sound.

in a preferred embodiment of my invention, the reproducing arm is mounted on a spring, which performsthe double function of supporting the arm and resiliently holding it in normal predetermined position. This spring. in its simplest form. is a flat blade held fast at its ends. and the arm is secured to the middle of the spring. "he

mounting of the spring is such that it is capable of a twisting or torsional movement to permit ready vibration of the arm laterally from its normal position in either direction. the same time, the spring fully takes 5 up the longitudinal thrust or strain exerted on the man during its operation. This re silient mounting of the vibratory arm produces a, construction of great simplicity. as it obviates the necessity of separate restoring or centralizing springs.

One of the marked advantages of my electric reproducer results from the extreme lightness and correspondingly low inertia of the vibratory unit, whereby the same rei. sponds freely and correctly to the mechanical actuations of the vibratory arm. F urthermore. theelectromagnetic mechanism may be so constructed that the magnetic member on the arm exerts no appreciable magnetic drag or lag on the arm, thereby enhancing the degree of faithfulness of reproduction.

The instrument of my invention is of special advantage in reproducing from phonograph records having several hundred lines to the inch and playing for half an ELECTRIC PHONOGRAPH REPRODUCER.

EISSUED hour or more. In these records, the walls of adjacent grooves are necessarily frail, and the needle vibrations are of extreme delicacy. With such finely grooved records, an ordinary mechanical reproducer having a stiff diaphragm of essentially high inertia is outof the question. The same objection applies, at least to a large extent, to a microphonic reproducer in which a diaphragm operates against packed resistance granules. Now, in the reproducer of my invention. there is no diaphragm, the vibratory unit is very light and of low inertia, so that it responds instantly and faithfully to the needle vibra- I tions. Since these vibrations are transmitted 70 to the magnetic member in amplified ratio, the slightest movements of the needle cause current impulses to be generated by this member.

In the accompanvin Serial No. 78,279.

drawings I have illustrated several embodiments of myjnvention. which T shall now describe in detail, so that those skilled in the art may understand the same. I want to make it clear, however, that these constructions are merely practical examples and not limitations of my invention. In these drawings,

Fig. 1 shows an interior face view, partly in section, of a phonograph reproducer constrnctsd in accordance with my invention;

Fig. 2 represents a cross-section on the broken line 2-2 of Fig. 1;

F ig. 3 is a top plan view in section on the broken line 33 of Fig. 1; V

Fig. 4. is a side view of a modified form of spring mounting for the needle arm;

Fig. 5 is a cross-section approximately on the broken line 5-5 of Fig. 4;

Fig. 6 is a cross-section on line 66 of Fig. 5; 95

Fig. 7 illustrates a side view, partly in section, of a modified form of reproducer embodying my invention; and

Fig. 8 represents a plan view of the con struction shown in Fig. 7

Before going into a detailed description of these drawings, let me explain that the various parts have been purposely exaggerated in proportion and spacing, so as to make the drawings as clear as possible. The actual 105 device would be considerably smaller than the illustrations.

I shall first describe the construction shown in Figs. 1, 2 and 3. The various parts of the instrument are mounted in a casing 110 plate 1, a body section 2, and a front plate or cover 3. These parts are preferably made separate and removably secured together by screws 4, or other fastening means. The casing partsmay be constructed of hght,

non-magnetic material, such as ,aluminum,

or an aluminum alloy. or they may be shaped out of bakelite or other suitable insulating composition. In the latter instance, the parts 1 and 2 could be molded asa single cup-shaped piece. The back plate 1 of the casing 1s provided with a hub 5 for mounting the instrument as a whole on a suitable arm 6. Since the particular embodiment I am describing is shown in the form of a phonograph reproducer, the arm 6 is supposed to be properly mounted to allow the reproducer to travel over a record.

Within the casing C is mounted a magnet M preferably of the permanent type. The magnet may be solid or composed of thin laminations. In the present instance, the magnet M is fixed to the back plate 1 by means of screws 7 but it may be supported in the casing in any other practical way. As seen from Fig. 1, the ma net is U-shaped and follows 'closely the out ines of the rectangular body section 2 of the easinggthus roviding a magnetic path of maximum ength in a small space. The legs of the magnet are bent forwardly, as indicated at 8, and then turned upwardly to form the polar ends 9. To each polar end is secured a U-shaped pole piece 10, as best shown in Fig. 3. Thesepolar pieces are made preferab y of soft iron, solid or laminated, and are firmly secured to the magnet by screws 11 or otherwise. Each pole piece 10 has a pair of limbs 12 and 13, which extend toward each other to form a pair. of transversely ali ned airgaps 14 and 15. On one or. both poIar limbs 12 is mounted a coil or coils 16. In the present instance, the coil 16 consists of two windings electrically connected, as indicated at 17, so as to form in effect a single coil. If the coil or coils 16.pro 'ect beyond the width of the body section 2 of the casin the front plate or cover 3 is formed with a bulge 18 to accommodatethe coils, but the magnetic structure with its pole pieces and coils may be so designed that a comparatively shallow casing will house all the girts. It will be noticed that the magnet may be fully equipped with the ole ieces 10 and the coil or coils 16 beore eing inserted into the casing. The central body section 2 of the casing is pro'videdat its lower end with a pair of transversely aligned lugs 19,, having each a slot 20 for receiving the ends of a spring blade 21, which is fixed in position by screws 22 or otherwise. At or near the center of the spring blade 21 is fixed a needle arm 23 inany practical way, as by means of a rivet 2 4. The arm 23 projects into the casing through a slot 25, and the lower end of the arm is formed as a needle holder 26 of any suitable construction adapted to hold a phonograph needle 27. The spring 21 is ,made of suitable spring metaland is so proportioned as to be capable of twisting or torsional movements at the center where the vibratory arm 23 is attached.

By looking at Fig: 2, it will be seen that whenthe needle of the reproducer rests on a record in playing position, thelongitudt nal thrust against the arm 23 is in the plane of the flat spring blade 21, and is therefore readily taken u .by the spring. \Vhen the needle vibrates laterally (as viewed in Fig. 2), the leaf spring 21 is twisted sideways at the center and the'needle arm 23 is allowed to vibrate back and forth in the casing. In other words, the leaf spring 21 not only supports the needle arm against longitudinal movement, but also constitutes a solid pivot bearing for the needle arm. Furthermore, the spring support 21 normally holds the arm 23 in a neutral position, so that the arm is readily vibrated in opposite directions from its normal position. The .part 21, therefore performs a triple function and A thus simplifies the construction.

' On the free orinner end of needle arm 23 is mounted an armature 28, which is a soft iron piece of the proper dimensions, depending upon the shape and size of the magnetic airgaps 14; and" 15. The armature 28 is preferably so dimensioned that it spans the airgaps 14' and 15; (1 is only of slightly less width than't'hcse airgaps. In Figs. 2 and 3, I have shown the armature 28 slightly overlappingthe polar limbs 12 and 13 at its ends. The torsional spring support 21 normally holds the armature 28 in a practically neutral position midway between the airgaps 14 and 15. That is to say, the armature is normally balanced by the opposing magnetic pulls at its ends, sothat the arm 23 is normally free from any strain or pull in the plane of its vibrations. This is easily understood from Fig.

It will be clear that as the needle arm 23 vibrates back and forth, the magnetic flux passing through the coil or coils 16 is correspondingly varied. That is to say, ,when

.the armature moves toward the airgap 14, the greater portion of the field flux passes through the polar limbs 12 and the coil or coils 16. When the armature 26 moves into a the airgap 15, the greater part of the field flux is shunted through the polar limbs 13,

whereby the flux passing through the windings 16 is decreased; The amount of variation of the number of lines of force passing through the coil or coils 16 depends upon the amplitude of vibration of the armature 28,

and the rate of magnetic varition depends upon the frequency of vibration of the arma- I have shown a pair of insul This places the [from the ture. through the current generating coils 16 is in amplified relation to the movements of.

the armature 28 for this reason: when the armature moves away from one pair of polar limbs, it simultaneously approaches the other polar limbs, so that the magnetic flux is suddenly shunted out of one pair of polar limbs into the other, and this sudden increased variation has an amplifying effect on the coil 16. Furthermore, since the armature 28 is at a considerably greater distance from the spring support 21 than is the point .of the needle 27, the vibrationsof the needle are transmitted to the armature in amplilied ratio, so that the minutcst vibrations of the needle produce movements of the armature sufiicient to generate current impulses in the coil or coils mounted on the magnet. In order to maintain the vibrating armature 28 in complete alignment with the polar limbs 12 and 13, the upper and lower surfaces of the polar li mbs and armature may be curved on the arc of a circle struck up from the axial center of the spring plate 21. This curvature of the polar limbs and armature is indicated in Fig. 2. This detail, however, is not necessary, since the armature vibrations are comparatively small.

The coil'or coils 16 are connected in a circuit leading to suitable amplifying apparatus, which need not be shown or described, since itforms no part of my invention and is furthermore well understood by those skilled in the art. In Figs. 1 and 2, ated binding posts 29, to which the ends 16 of the windings 16 are connected. If the supporting arm 6 is tubular, the circuit connections 30 leading from the binding posts 29 may be concealed within this llflllOW arm. thereby imparting a neater appearance to the phonograph as a whole.

In Figs. 4, 5 and 6, I have shown a modified form of spring support for the vibratory needle arm. In this construction. the spring blade 21' is given an initial torsional tension by slightly twisting the ends in opposite directions, as indicated at 31 and 32. central section of the spring in a neutral or balanced condition, and to this balanced section of the spring is. secured a needle arm 33 of proper shape and dimensions. A convenient way of attaching the needle arm to the spring is by providing the arm with a recess 34 in which the spring 21 is tightly fitted. A plate 35 is then placed over the spring, and a screw or other fastening member 36 rigidly secures the parts together. The ends may be mounted in any suitable Way to give them the desired degree of initial tor= sional' tension. .By way of example, I have shown a pair of lugs 37 and 38 projecting lower end of the casing, similar 31 and 32 of spring 2 The variation of the magnetic flux to the lugs 19 of Figs. 1 and 2. The lugs 37and 38 are provided each with a slot 39 of a configuration as shown in Fig. 4. That is to say. each slot 39 has a lower narrow portion 40 and an enlarged portion formed by a slanting side 41. In the lugs 37 and 38 are mounted set-screws 42 and 43 arranged to project into the enlarged portions of the slots 39. The ends of spring 21 fittight into the narrow portions 40 of these slots. If desired, small end plates 44 may be secured to the lugs 37 and 38 across the narrow portions 40 of the slots, so as to positively lock the spring 21 against accidental movement in a longitudinal direction. The set-screws 42 and 43 bear against the ends of the spring at or near the upper edge thereof, whereby these ends may be flexed laterally in the enlarged portions of the slots 39. This will be clearly understood from Fig. at. The slots 39 are arranged oppositely in the lugs 37 and 38; in other words, the slanting sides 41 of the slots are positioned reversely with respectto the spring ends. By adjusting the screws 42 and 43, the initial lateral twist or turn given the spring ends may be regulated to the proper degree, so that the needle arm 33 is normally held balanced in predetermined position. The opposing torsional strains at the ends of spring 21 permit ready vibrations of the needle arm laterally of the spring, as previously explained in reference to spring arm 23 of Figs. 1 and 2. The spring support of Figs. 4, 5 and 6 may be considered to be substituted in Figs. 1 and 2, but in the broader aspect of my invention, any practical electromagnetic reproducing mechanism may be associated with my novel con- StlllCtlOIi of spring support for the needle arm.

In the modification of Figs. 7 and 8, there is a permanent U-shaped magnet M secured to .the back wall of a casing C of proper construction and design. To t-he'ends of magnet M are secured forwardly projecting pole pieces 45, usually made of soft iron, and one or both of these pole pieces carry a winding 46. If two windings 46 are used. as shown in Fig. 8,, they are connected in series so as to constitute a single coil. When I speak of the coil 46, therefore. I mean either one or more windings. The pole pieces 45 are separated by an ail-gap 47. in which vibrates an armature 48 attached to the inner end of a needle arm 49. The armature 48 is a piece of soft iron of the proper dimensions, so as to fitclosely in the airgap 47 without touching the pole pieces. The armature 48 is normally held in a position in which it projects part way into the ail-gar.) 47. Consequently, when the needle arm 49 vibrates in one direction the armature 48 moves farther into the airgap to increase the magnetic flux through the coil 46. During the reverse movement of the needle arm, the armature moves further out of the airgap and thereby decreases the magnetic fiux through the winding. The needle arm 49 is mounted 1n any practical way on the casing C. In the present instance, this arm is pivoted at 50 by a hearing at the lower side of the casing. It will be observed that the vibrationsof the needle attached to arm 49 are transmitted in amplified ratio to the armature 48. Sui-table spring means, such asa pair of leaf springs 51..hold the needle arm'in normal position. In place of the pivot bearing 50 and the centering springs 51, the combined supporting and centralizing spring 21 or 21 may be used.

Attention is called to the fact that the armatures 28 and 48 are so arranged in the magnetic airgaps that any tendency ofthe pole pieces to attract the armature laterally is at right angles to the plane of vibration of the needle arm. Consequently, any lateral magnetic drag that may develop by reason of the armature being slightly closer to one pole piece than to the other, exerts no drag or load (certainly to no disturbing extent) on the vibrations of the needle arm. Furthermore, any magnetic side pull on the armature (and therefore on the needle arm) is fully taken up by the mounting of the arm, particularly if the spring support 21 or 21' is used.

Another practicaladvantage of my construction lies in the fact that the flux variations produced by the vibratory armature take place in the soft iron pole pieces and not in the steel body of the magnet. This increases the sensitiveness of the instrument, because soft ,iron has greater magnetic permeability than" steel and offers little resistance to changes in magnetic flux.

It will be seen from the foregoing description that I have provided an electric sound reproducer of exceedingly simple construction and capable of faithfully reproducing the most delicate vibrations of a phonograph needle. Of course, it is assumed that the parts are pro erly designed proportioned and assemble No rule can be laid down as to the precise dimensions of the parts, for these are matters of experiment well within the skill of the artisan trained in this particular line of science.

In the broader aspect of my invention, the vibratory arm or lever which carries the armature may be mechanically actuated at its outer end by other means than a phonograph needle. It is possible, for example, to connect a transmitting diaphragm with or to the outer end of the needle arm, and if this diaphragm is actuated by sound waves, the armature 28 or 48 is vibrated to generate current impulses in the associated cell for acoustically reproducing the sound waves which. set the transmitting diaphragm in' motion. In this way, my new instrument I may be used as a telephone transmitter capable of use in broadcasting and similar fields of utility.

Although I have shown and described certain specific constructions. it is apparent that the various features of my invention may be mechanically embodied in other forms without departing from the scope of the following claims.

When I refer to my invention as a phonograph reproducer, I use the word phonograph in its broadest possible sense of recorded sound. The particular type or name of sound-reproducing machine in which my invention is embodied, is immaterial.

What I claim as my invention is:

1. In an electric phonograph reproducer free from an acoustic diaphragm, a vibratory lever adapted to be actuated by the vibrations of a record needle, said lever comprising a short arm and a long arm, a permanent magnet having pole pieces, a magnetic member mounted on the free end of said long arm in operative relation to said pole pieces, whereby the needle vibrations are transmitted in amplified ratio to said member, non-acoustic resilient means for holding said needle arm and magnetic member in predetermined normal position, and a current-generating coil controlled by the movement of said member.

2. An electric phonograph reproducer comprising a casing, a substantially U- shaped magnet mounted in said casing with its legs extending upwardly so that the pole pieces terminate near the upper end of the casing, a needle arm pivoted to the lower end of said casing, the pivot point of said needle arm being arranged that the needle vibrations are transmitted to the inner end of the arm in amplified ratio, an armature mounted on the inner end of said needle arm to vary the magnetic flux through said pole pieces, and a coil on one of said pole pieces.

3. In an electric sound reproducer, a magnet provided with two pairs of oppositely arranged pole pieces forming. a pair of aligned airgaps, said pole pieces and airgaps constituting two parallel paths for the magnetic flux, a' pivoted lever adapted to be actuated at one end, an armature mounted on the otherzend of said lever and arranged to reciprocate between said airgaps, so that one end of said armature moves toward one of the airgaps while the other end moves away from the other airgap, whereby the magnetic flux is increased through one of said parallel paths and simultaneously decreased through the other path, and'a coil eifected by flux variations through said paths.

4. In an electric phono aph reproducer, a casing, a magnet secure to a wall of said casing, said magnet consisting of a substan-- tially U-shaped body lying fiat against said Wall and having a pair of .polar projections extending away from said wall, said magnet being so mounted that the legs thereof extend upwardly so that the polar projections are near they upper part of said casing, said pole promotions being arranged to provide an airgap, a coil on at least one of said polar projections, a needle arm pivoted to the lower part of said casing and extending upwardly toward said polar projections, anarmature mounted on the inner end of said arm to vibrate in said airgap in amplified relation to the needle vibrations, and non-acoustic resilient means for holding said needle arm and armature in predetermined normal position.

5. An electric phonograph reproducer comprising a casing, a needle arm pivoted to the lower portion of said casing so as to vibrate transversely thereof, an armature mounted on the free inner end of said arm which terminates near the upper'portion of said casing, so that the needle vibrations are transmitted in amplified ratio to said armature, the vibrations of said armature being in a plane at right angles to the plane of said casing, and electromagnetic mechanism,

mounted within said casing for generatin currents in accordance with the amplifie vibrations of said armature.

6. An electric phonograph reproducer comprising a shallow casing having substantially parallel front and rear walls, a

magnet mounted in said casing against one of said Walls and having an airgap near the upper portion of said casing, a needle arm pivoted to the lower portion of said casing so as to vibrate transversely thereof between said walls, a magnetic member mounted on the inner end of said arm to vary the flux across said airgap, and a current-generating,

coil controlled by the vibrations of said magnetic member. s

7. In an electric phonograph reproducer, a casing provided at its lower end with a pivoted needle-holder, a vibratory arm arranged within said casing and connected at its lower end with said needle-holder, a magnet so mounted in said casing that the magnetic airgap is near the upper end of the casing diametrically opposite said needle-holder, a coil, associated with said magnet, and a 'magnetic member mounted on the free end of said arm to vibrate in operative relation to said airgap, the length of said arm being such that the needle vibrations are transmitted to said magnetic I ,member in amplified ratio to generate variable currents in the circuit of said coil.

8. An electric phonograph reproducer comprising a shallow casing having substantially parallel front and rear walls, a magnet mounted in said casing against one of said walls and having polar faces arran d to form a pair of aligned airgaps extending transversely of said casing ina direction at right angles to the walls thereof, a needle arm pivoted to said casing so as to vibrate in a plane perpendicular to said walls,.an armature connected to the free end of said needle arm and arranged to vibrate between said airgaps transversely of the casing in a path substantially parallel with said polar faces, and a coil controlled by said armaure. v

9. In an electric sound reproducer, a magnet having a pair of U-shaped pole pieces arranged to provide a pair of aligned airgaps, a coil surrounding the limb of one of said pole pieces, a pivoted lever comprising 'a short arm and a long arm, acoustic means for mechanically vibrating said short arm and an armature attached to the free end of said long arm'to vibrate between said airgaps in amplified relation to the movements of the short arm. l

10. An electric phonograph reproducer comprising a casing, a magnet mounted in said casing and having a pair of U-shaped pole pieces arranged to provide a pair of airgaps near the upper portion of the casing, said airgaps extending in axial alignment transversely of said casing, a needle arm pivoted to the lower portion of said casin in such position that the longer section of t e needle arm extends toward said ole pieces in a. direction midway of said air aps, said needle arm vibrating transverse y of said casing, an armature mounted on the free inner end of the needlearm to vibrate between said airgaps and thereby vary the magnetic flux through'said coil, the needle vibrations of said arm being transmitted in amplified ratio to said armature, and means for normally holding said armature substantially midwa of sad airgaps.

11. 11 an electric sound reproducer a magnet having pole pieces arranged to provide a pail-"of parallel magnetic paths with aligned airgaps, an armature arranged to vibrate between said air-gaps in a direction at right angles to the passage of flux across said airgaps, so that the vibrations of said armature increase the magnetic field flux through one of said parallel aths and simultaneously decrease the flux t rough the other path, an acoustically actuated member for vibrating said armature, and a coil subJect to the flux variations in one of said aths 12. In an electric phonograph repro ucer; a magnet having pole pieces arranged to provide apair of parallel magnetic paths so as to lie in a plane practically at right angles to of said parallelaths and simultaneously decrease the flux t rough the other path, and a coil mounted on one of said pole pieces.

13. In an electric sound re roducer, a magnet having a pair of U- aped pole piecesarranged to provide a pair of aligned airgaps, a coil surrounding t e limb of one of said pole pieces, a vibratory lever comprising a short arm and a long arm, a torsional resilient spring blade for pivotally supporting said lever, acoustic means for mechanically vibrating said short arm, and an armature attached to the free end of said long arm to vibrate between said airgaps in amplified relation to the movements of the short arm, said supporting spring normally holding said armature substantially midway of said airgaps.

14. In a phonograph reproducer, a later ally twistable spring blade supported at its ends, and a needle arm secured to and supported by said blade which also forms a solid pivot bearing for said arm.

15. In a phonograph reproducer, a flat torsional spring blade supported at its ends the plane of a playing record, a needle arm attached to and supported by said spring, and means for placing said spring under initial torsional strain by laterally displaqing the ends thereof in opposite directions to hold said arm resiliently in normal predetermined position.

16. A phonograph reproducer having a solid spring blade supported at it's ends and capable of lateral twisting movements in opposite directions at its central portion, a needle arm attached to said blade at or near the center thereof, so that said blade not only supports said arm against longitudinal movement but also constitutes the sole pivot bearing for the lateral vibrations of said arm, and a reproducing element operated by said arm.

17 In a phonograph torsional spring blade supported at its ends so as to lie in a plane practically at right angles to the plane of a playing record, and

reproducer, a flat a needle arm attached to said spring and supported solely thereby, said sprin blade also constituting the sole hearing %or the pivotal movements of said arm.

18. In a phonograph reproducer, a twistable spring blade sup orted at its ends in bearings, means for a justing said bearings laterally of said spring blade in opposite directions to place the same under initial torsional strain, and a needle arm secured to the center of said blade and supported thereby against longitudinal movement, said blade also forming a pivotal bearing for said arm.

19. An electric sound reproducer comprising a magnet having polar faces arranged to provide a pair of aligned airgaps through which the normal field flux passes in parallel paths, a vibratory arm, an armature carried by said arm, means for pivotally supporting said arm independently of said armature, which is arranged to reciprocate between said airgaps for decreasing the magnetic reluctance across one airgap and simultaneously increasing the magneticreluctance across the other airgap, said armature being mounted to vibrate in a path substantially parallel with said polar faces, and a coil controlled by said flux variations to generate current impulses in accordance with the vibrations of said arm.

20. A phonograph reproducer comprising a casing mounted to travel over a record, a spring lade fixed at its ends to said casing and arranged in a plane substantially at right angles to the axis of said casing, whereby said blade is positioned approximately edgewise with respect to a playing 'record, a needle arm attached to the middle of said blade and extending in substantially the plane thereof, so that the longitudinal thrust of said arm is practically in or along the plane of said blade, which thus acts as a firm pivot for said arm and yet permits vibration thereof, and reproducing mechanism operated by said arm.

ADOLPH A. THOMAS. 

